Leads for substrates that are pushed onto an edge of the substrate have been formed with a spring clip on each lead, which engages the top and bottom surfaces of the substrate to hold the lead in its desired location. Resilient fingers of the clip grip opposing sides of the substrate by spring tension between the lead and the substrate, with the lead in contact with a conductive area or contact pad on the substrate. One or both of the fingers of each lead may hold a solder mass, to be positioned at the contact pad, to which it becomes soldered upon application of heat and subsequent cooling. Such arrangements are shown in the prior art illustrated by U.S. Pat. Nos. 4,605,278; 4,597,628; 4,679,889; 4,697,865 and 4,428,305 of the present inventor.
Certain difficulties have been associated with the prior art applications of leads to substrates which are overcome or avoided by the present invention. Some substrates have contact pads on one surface of a substrate that are closely spaced. Other substrates have sets of contact pads adjacent the substrate edge on both opposing surfaces of the substrate, with the two sets of contact pads offset from each other, i.e. a contact pad on one side is between two pads on the opposing surface along the edge of the substrate. With the present trend toward having more and more leads attached to a substrate, leads to be attached to the substrate must have extremely close spacing between adjacent leads. Desirable known constructions for holding solder to a lead have tabs that initially extend laterally from the side edges of the leads and are then bent to hold the solder. With conventional lead arrangements, the lead spacing becomes too close to allow for these laterally extending solder-holding structures.
One arrangement that has partially solved these problems is shown in U.S. Pat. No. 4,737,115 of the present inventor. In that patent, two sets of leads are formed to extend from opposite edges of a central carrier strip. Once folded over, the leads become interleaved to form a single row of leads. The solder is held on the lead tip without the laterally extending structures. By applying pressure to the leads, the two sets of leads separate to receive a substrate edge between them, suitable for substrates with staggered contact pads on opposed faces. This arrangement partially avoids the described problem by eliminating the laterally extending tabs, but does not permit taking advantage of the desirable features of the lateral tabs. Further, this arrangement can not be used with closely spaced contact pads on the same substrate surface.
There also exists a need for a solderable lead construction that is both easy to manufacture as well as being easy to assemble onto multiple contact pads of a substrate with stable retention on the substrate during a soldering process.